[Mesa-dev] [PATCH] i965: Fix move_interpolation_to_top() pass.

[Kenneth Graunke]

The pass I introduced in commit a2dc11a7818c04d8dc0324e8fcba98d60bae
was entirely broken.  A missing "break" made the load_interpolated_input
case always fall through to "default" and hit a "continue", making it
not actually move any load_interpolated_input intrinsics at all.
It would only move the simple load_barycentric_* intrinsics, which
don't emit any code anyway, making it basically useless.

The initial version I sent of the pass worked, but I apparently
failed to verify that the simplified version in v2 actually worked.

With the obvious fix applied (so we actually tried to move LIIs),
I discovered a second bug: we weren't moving the offset SSA def
to the top, breaking SSA validation.

The new version of the pass actually moves load_interpolated_input
intrinsics and all their dependencies, as intended.

Papers over GPU hangs on Ivybridge and Baytrail caused by the
recent NIR FS input rework by restoring the old behavior.
(I'm not honestly sure why they hang with PLN not at the top.)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97083
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_fs.cpp | 49 ++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 21 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index f9af525..bcd08ac 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -6353,38 +6353,45 @@ move_interpolation_to_top(nir_shader *nir)
          continue;
 
       nir_block *top = nir_start_block(f->impl);
+      exec_node *cursor_node = NULL;
 
       nir_foreach_block(block, f->impl) {
          if (block == top)
             continue;
 
-         nir_foreach_instr_reverse_safe(instr, block) {
+         nir_foreach_instr_safe(instr, block) {
             if (instr->type != nir_instr_type_intrinsic)
                continue;
 
             nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
-            switch (intrin->intrinsic) {
-            case nir_intrinsic_load_barycentric_pixel:
-            case nir_intrinsic_load_barycentric_centroid:
-            case nir_intrinsic_load_barycentric_sample:
-               break;
-            case nir_intrinsic_load_interpolated_input: {
-               nir_intrinsic_instr *bary_intrinsic =
-                  nir_instr_as_intrinsic(intrin->src[0].ssa->parent_instr);
-               nir_intrinsic_op op = bary_intrinsic->intrinsic;
-
-               /* Leave interpolateAtSample/Offset() where it is. */
-               if (op == nir_intrinsic_load_barycentric_at_sample ||
-                   op == nir_intrinsic_load_barycentric_at_offset)
-                  continue;
-            }
-            default:
+            if (intrin->intrinsic != nir_intrinsic_load_interpolated_input)
+               continue;
+            nir_intrinsic_instr *bary_intrinsic =
+               nir_instr_as_intrinsic(intrin->src[0].ssa->parent_instr);
+            nir_intrinsic_op op = bary_intrinsic->intrinsic;
+
+            /* Leave interpolateAtSample/Offset() where they are. */
+            if (op == nir_intrinsic_load_barycentric_at_sample ||
+                op == nir_intrinsic_load_barycentric_at_offset)
                continue;
-            }
 
-            exec_node_remove(&instr->node);
-            exec_list_push_head(&top->instr_list, &instr->node);
-            instr->block = top;
+            nir_instr *move[3] = {
+               &bary_intrinsic->instr,
+               intrin->src[1].ssa->parent_instr,
+               instr
+            };
+
+            for (int i = 0; i < 3; i++) {
+               if (move[i]->block != top) {
+                  move[i]->block = top;
+                  exec_node_remove(&move[i]->node);
+                  if (cursor_node)
+                     exec_node_insert_after(cursor_node, &move[i]->node);
+                  else
+                     exec_list_push_head(&top->instr_list, &move[i]->node);
+                  cursor_node = &move[i]->node;
+               }
+            }
          }
       }
       nir_metadata_preserve(f->impl, (nir_metadata)
-- 
2.9.0